Fair Value of Assets and Liabilities - Summary Of Changes In Level 3 Assets And Liabilities Measured At Fair Value (Details) - Level 3 - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ (18)	$ (19)	$ (14)	$ (23)
Acquired		0		0
Total net gains (losses) included in net income	0	0	(9)	(1)
Purchases	0	0	0	0
Sales	0	0	0	0
Settlements	2	2	7	7
Net transfers into (out of) Level 3	0	0	0	0
Ending balance	(16)	(17)	(16)	(17)
Net unrealized gains (losses) included in net income	0	0	(9)	(1)
Trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		1		1
Acquired		0		0
Total net gains (losses) included in net income		0		0
Purchases		0		0
Sales		0		0
Settlements		0		0
Net transfers into (out of) Level 3		0		0
Ending balance		1		1
Net unrealized gains (losses) included in net income		0		0
Interest- only strips- AFS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	30	25	32	19
Acquired		0		0
Total net gains (losses) included in net income	1	(1)	5	(4)
Purchases	0	0	0	5
Sales	(35)	0	(68)	(8)
Settlements	0	0	0	0
Net transfers into (out of) Level 3	20	9	47	21
Ending balance	16	33	16	33
Net unrealized gains (losses) included in net income	0	1	0	3
Loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	25	13	12	14
Acquired		0		0
Total net gains (losses) included in net income	0	0	2	1
Purchases	3	0	8	0
Sales	(8)	0	(18)	0
Settlements	0	(1)	(2)	(3)
Net transfers into (out of) Level 3	4	0	22	0
Ending balance	24	12	24	12
Net unrealized gains (losses) included in net income	0	0	2	1
Loans held for investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		0	16	0
Acquired		13		13
Total net gains (losses) included in net income		0	0	0
Purchases		0	0	0
Sales		(3)	0	(3)
Settlements		(2)	(2)	(2)
Net transfers into (out of) Level 3		4	(14)	4
Ending balance	$ 0	12	0	12
Net unrealized gains (losses) included in net income		$ 0	$ 0	$ 0

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Acquisition

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Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Acquisition

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No definition available.

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Amount of unrealized gain (loss) recognized in income for derivative asset (liability) after deduction of derivative liability (asset), measured at fair value using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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